Waveguide for an augmented reality or virtual reality display

Abstract

A waveguide ( 1 ) for use in an augmented reality or virtual reality display, comprising: an output diffractive element comprising a plurality of optical structures ( 22, 28, 26 ) in a photonic crystal; a first major surface of the waveguide, and a second major surface of the waveguide, the first major surface separated in a direction perpendicular to a plane of the waveguide from the second major surface, wherein light propagates along the waveguide towards the output diffractive element by undergoing total internal reflection between the first and second major surfaces wherein the plurality of optical structures ( 22, 28, 26 ) are arranged in a plane of the waveguide in an array which is configured to receive light from an input direction and diffract the light into a plurality of orders, some of the orders being diffracted in the plane of the waveguide at an angle to the input direction to provide 2D expansion across the plane of the waveguide, and other orders being out-coupled in a direction perpendicular to the plane of the waveguide towards a viewer; wherein at least one of the optical structures ( 22, 28, 26 ) of the plurality of optical structures ( 22, 28, 26 ) has a profile in a direction that is perpendicular to the plane of the waveguide, wherein the profile varies along one or more directions parallel to the plane of the waveguide, such that the out-coupled orders are provided preferentially from the first major surface of the waveguide compared to the second major surface of the waveguide.

The invention claimed is: 
     
         1 . A planar slab waveguide for use in an augmented reality or virtual reality display, comprising:
 an input diffractive optical element;   an output diffractive element comprising a plurality of optical structures in a photonic crystal, wherein the optical structures have a different refractive index to a surrounding waveguide medium, wherein the input diffractive optical element couples light towards the plurality of optical structures along an input light path;   a first major surface of the planar slab waveguide, and a second major surface of the planar slab waveguide, the second major surface parallel to the first major surface, wherein light propagates through the planar slab waveguide along the input light path towards the output diffractive element by undergoing total internal reflection between the first and second major surfaces;   wherein the plurality of optical structures are arranged in a plane of the planar slab waveguide parallel to the first major surface and the second major surface in an array which is configured to:
 receive light from the input light path; 
 diffract a first portion of the light into an angle relative to the input light path to provide 2D expansion across the plane of the planar slab waveguide; and 
 diffract a second portion of the light out of the plane of the planar slab waveguide, 
   wherein at least one of the optical structures of the plurality of optical structures has a height in a direction that is perpendicular to the plane of the planar slab waveguide, wherein the height varies along one or more directions parallel to the plane of the planar slab waveguide, thereby causing the second portion of light to be diffracted preferentially from the first major surface of the planar slab waveguide, compared to the second major surface of the planar slab waveguide.   
     
     
         2 . The planar slab waveguide of  claim 1 , wherein the height of the at least one of the optical structures of the plurality of optical structures varies continuously along the one or more directions parallel to the plane of the planar slab waveguide. 
     
     
         3 . The planar slab waveguide of  claim 1 , wherein the at least one of the plurality of optical structures has a discontinuity in its height. 
     
     
         4 . The planar slab waveguide of  claim 3 , wherein the at least one of the plurality of optical structures comprises a plurality of discontinuities. 
     
     
         5 . The planar slab waveguide according to  claim 1 , wherein a variation in height of at least some of the plurality of optical structures is different to the variation in height of others of the plurality of optical structures. 
     
     
         6 . The planar slab waveguide according to  claim 5 , wherein a first subset of optical structures from the plurality of optical structures in a first region of the planar slab waveguide comprise a first variation in height of optical structures and a second subset of optical structures from the plurality of optical structures in a second region of the planar slab waveguide comprise a second variation in height of optical structures different from the first variation in height, and the first region being displaced from the second region along the plane of the planar slab waveguide. 
     
     
         7 . The planar slab waveguide according to  claim 5 , wherein the input light path defines a first axis in the plane of the planar slab waveguide, and the one or more directions through which the optical structures vary in height is at an angle to the input light path. 
     
     
         8 . The planar slab waveguide according to  claim 7 , wherein a first subset of optical structures from the plurality of optical structures in a first region of the planar slab waveguide comprise a first variation in height of optical structures and a second subset of optical structures from the plurality of optical structures in a second region of the planar slab waveguide comprise a second variation in height of optical structures, wherein the direction through which the first subset of optical structures vary in height is at a first angle to the input light path and the direction through which the second subset of optical structures vary in height is at a second angle to the input light path, wherein the first region and the second region are separated by a line formed along the input light path extending from a point at which light is incident at the output diffractive element. 
     
     
         9 . The planar slab waveguide according to  claim 1 , wherein at least one of the plurality of optical structures is arranged such that the height of the at least one optical structure has a negative gradient in a direction away from a point at which the light is incident on the at least one optical structure. 
     
     
         10 . The planar slab waveguide according to  claim 1 , wherein at least one of the plurality of optical structures is arranged such that the height of the at least one optical structure has a positive gradient in a direction away from a point at which the light is incident on the at least one optical structure. 
     
     
         11 . The planar slab waveguide of  claim 1 , wherein the plurality of optical structures, respectively, have a shape, when viewed in the plane of the planar slab waveguide, comprising a plurality of substantially straight sides having respective normal vectors at different angles. 
     
     
         12 . An augmented reality or virtual reality display, comprising:
 a planar slab waveguide comprising:
 an input diffractive optical element to couple light into the planar slab waveguide; and 
 an output diffractive element including a plurality of optical structures in a photonic crystal, wherein the optical structures have a different refractive index to a surrounding waveguide medium, wherein the input diffractive optical element couples light towards the plurality of optical structures along an input light path; 
 a first major surface of the planar slab waveguide, and a second major surface of the planar slab waveguide, the second major surface parallel to the first major surface, wherein light propagates through the planar slab waveguide along the input light path towards the output diffractive element by undergoing total internal reflection between the first and second major surfaces; 
 wherein the plurality of optical structures are arranged in a plane of the planar slab waveguide parallel to the first major surface and the second major surface in an array which is configured to:
 receive light from the input light path; 
 diffract a first portion of the light into an angle relative to the input light path to provide 2D expansion across the plane of the planar slab waveguide, and 
 diffract a second portion of the light out of the plane of the planar slab waveguide; 
 
 wherein at least one of the optical structures of the plurality of optical structures has a height in a direction that is perpendicular to the plane of the planar slab waveguide, wherein the height varies along one or more directions parallel to the plane of the planar slab waveguide, thereby causing the second portion of light to be diffracted preferentially from the first major surface of the planar slab waveguide, compared to the second major surface of the planar slab waveguide. 
   
     
     
         13 . The augmented reality or virtual reality display of  claim 12 , wherein the height of the at least one of the optical structures of the plurality of optical structures varies continuously along the one or more directions parallel to the plane of the planar slab waveguide. 
     
     
         14 . The augmented reality or virtual reality display of  claim 12 , wherein the at least one of the plurality of optical structures has a discontinuity in its height. 
     
     
         15 . The augmented reality or virtual reality display of  claim 14 , wherein the at least one of the plurality of optical structures comprises a plurality of discontinuities. 
     
     
         16 . The augmented reality or virtual reality display according to  claim 15 , wherein the input light path defines a first axis in the plane of the planar slab waveguide, and the one or more directions through which the optical structures vary in height is at an angle to the input light path. 
     
     
         17 . The augmented reality or virtual reality display according to  claim 16 , wherein a first subset of optical structures from the plurality of optical structures in a first region of the planar slab waveguide comprise a first variation in height of optical structures and a second subset of optical structures from the plurality of optical structures in a second region of the planar slab waveguide comprise a second variation in height of optical structures, wherein the direction through which the first subset of optical structures vary in height is at a first angle to the input light path and the direction through which the second subset of optical structures vary in height is at a second angle to the input light path, wherein the first region and the second region are separated by a line formed along the input light path extending from a point at which light is incident at the output diffractive element. 
     
     
         18 . The augmented reality or virtual reality display of  claim 12 , wherein a variation in height of at least some of the plurality of optical structures is different to the variation in height of others of the plurality of optical structures. 
     
     
         19 . The augmented reality or virtual reality display according to  claim 18 , wherein a first subset of optical structures from the plurality of optical structures in a first region of the planar slab waveguide comprise a first variation in height of optical structures and a second subset of optical structures from the plurality of optical structures in a second region of the planar slab waveguide comprise a second variation in height of optical structures different from the first variation in height, and the first region being displaced from the second region along the plane of the planar slab waveguide. 
     
     
         20 . A method of manufacture of a planar slab waveguide for an augmented reality or virtual reality display, the method comprising:
 providing a planar slab waveguide comprising an input diffractive optical element and an output diffractive element comprising a plurality of optical structures in a photonic crystal, wherein the optical structures have a different refractive index to a surrounding waveguide medium, wherein the input diffractive optical element couples light towards the plurality of optical structures along an input light path;   arranging the plurality of optical structures, wherein the planar slab waveguide comprises a first major surface of the waveguide, and a second major surface of the waveguide, the second major surface parallel to the first major surface, wherein light propagates through the planar slab waveguide along the input light path towards the output diffractive element by undergoing total internal reflection between the first and second major surfaces;   wherein the plurality of optical structures are arranged in a plane of the planar slab waveguide parallel to the first major surface and the second major surface in an array which is configured to:
 receive light from the input light path; 
 diffract a first portion of the light into an angle relative to the input light path to provide 2D expansion across the plane of the planar slab waveguide; and 
 diffract a second portion of the light out of the plane of the planar slab waveguide, wherein at least one of the optical structures of the plurality of optical structures has a height in a direction that is perpendicular to the plane of the planar slab waveguide, wherein the height varies along one or more directions parallel to the plane of the planar slab waveguide, thereby causing the second portion of the light to be diffracted preferentially from the first major surface of the planar slab waveguide, compared to the second major surface of the planar slab waveguide.